->''"So what now, Jack Sparrow? Are we to be two immortals locked in an epic battle until Judgment Day when trumpets sound?"''
-->-- '''Captain Barbossa''', ''Film/PiratesOfTheCaribbeanTheCurseOfTheBlackPearl''

A Mutual Disadvantage is a scenario in which two (or more) sides in a fight are unable to gain an advantage over each other due to both being equally disadvantaged against one another in either offensive or defensive abilities. This can come in two flavors;

* '''[[PaddedSumoGameplay Mutual Invulnerability]]''': Both participants are offensively disadvantaged - neither of them can harm the other, as they are both immune or resistant to each others' attacks. The result is a battle between two {{Stone Wall}}s, making for a stalemate unless and until someone else intervenes.
* '''[[RocketTagGameplay Mutual Weakness]]''': Both participants are extremely susceptible to each others' skills, essentially making it a fight between {{Glass Cannon}}s. The result is either a standoff wherein both sides try to avoid MutuallyAssuredDestruction, or a fight that could go either way, but is very likely to [[CurbStompBattle be one-sided]] in favor of whoever gets the first strike. Compare MexicanStandoff, where the stalemate is the result of the participants all being perfectly matched. Often happens in fights against {{Evil Counterpart}}s.

Note that any RPG system with pair-based ElementalRockPaperScissors will naturally display both types, with equal elements creating mutual invulnerability while opposing elements have mutual weakness.

LikeCannotCutLike and TakesOneToKillOne are {{Sub Trope}}s.


!!Mutual invulnerability:

[[folder: {{Anime}} and {{Manga}}]]
* In ''Manga/{{Bleach}}'', Hitsugaya and Halibel were both capable of transforming each other's attacks into their own, resulting in repeated [[NoSell No Sells]] against each other throughout much of their battle.
* In ''OnePiece'', Smoker and Ace proved unable to hurt each other, due to both being Logia Devil Fruit users with elements that do not naturally interact - Ace's flames equalized with Smoker's smoke - all they achieved was a huge pillar of smoke and fire. It happened again when Ace fought Kuzan and their respective fire and ice Devil Fruits powers nullified each other.
** Kuzan and Sakazuki fought for ''ten'' days on the island Punk Hazard to a stalemate because their Devil Fruits were opposing elements, ice and magma. In the end, they had used their powers so much the halves of the island inhabited by them got permanently altered into a frozen tundra and a volcanic wasteland. [[spoiler:Sakazuki eventually crippled Kuzan and won the battle.]]
* In ''Manga/FairyTail'', the fight between Natsu and Totomaru starts out this way. Totomaru has power over all flame, including that of his opponents, which allows him to redirect Natsu's attacks. Natsu is not only immune to fire [[FeedItWithFire but eats it to restore his strength]] Of course, Totomaru has the small advantage that one type of his fire smells (and tastes) horrible and makes Natsu gag. Natsu finally breaks the stalemate by making a fireball so big that Totomaru couldn't control it, though he still technically didn't "win": Natsu's goal was destroying the valuable piece of machinery Totomaru was guarding (which he did) and Totomaru went down from a sneak attack via the arrival of [[BigDamnHeroes Gray and Elfman]].

[[folder: {{Comics}}]]
* An issue of ''Billy Batson and the Power of Shazam''; [[ComicBook/{{Shazam}} Captain Marvel]] and ComicBook/BlackAdam are evenly matched and cannot harm each other; likewise [[DistaffCounterpart Mary Marvel]] and Black Adam Junior seem to be immune to each other's punches. [[spoiler:But Black Adam Junior '''can''' injure Captain Marvel.]]
* Havok and ComicBook/{{Cyclops}} in ''ComicBook/XMen'' comics. As they are brothers, this situation happens very rarely, but when it does, they are both immune to each other's attacks, because their powers work in the same way, and each can use the other's attack as an energy source. The same is true of Sean Cassidy (Banshee), and his cousin Thomas, neither's powers can affect the other. This is believed in both cases to be due to their genetic relationship and can apply to other related mutants as well.
* ''ComicBook/BatmanAndCaptainAmerica'': after ComicBook/TheJoker becomes [[EvenEvilHasStandards furious]] after finding out that his collaborator the ComicBook/RedSkull is a Nazi, the two villains try to use their own weaponized toxins on each other to no effect. Since both Joker and Red Skull are immune to their own toxins and both Joker Venom and Red Skull's "dust of death" are remarkably similar, both characters are also immune to ''each other's'' toxins.
* In Dynamite's ''Radio/TheShadow'' #7, the Shadow and Red Raja, having trained under the same old masters, NoSell each other's supernatural powers. They end up settling things in a SwordFight.

[[folder: {{Film}}]]
* ''Franchise/PiratesOfTheCaribbean'':
** Barbossa and Jack Sparrow fall into a mutual invulnerability version of this trope for a short while, during ''Film/PiratesOfTheCaribbeanTheCurseOfTheBlackPearl''.
** Again in ''Film/PiratesOfTheCaribbeanAtWorldsEnd'', though here imposed by terrain. Calypso hated both ships and their captains, so she created a huge typhoon that made maneuvering impossible (removing the Black Pearl's speed advantage) and made firing the cannons impossible (removing the Flying Dutchman's firepower advantage). Thus it came down to a brutal ship to ship fight between crews she hoped neither would survive.
* ''Film/TheMatrixRevolutions'': Neo has fully embraced his 'The One' status and therefore can do just about anything in the Matrix and can withstand an almost limitless amount of damage. Agent Smith has infected everyone, human or machine, in the Matrix and can also do anything and withstand anything.
* ''Film/TheGoldenVoyageOfSinbad''. The eternal battle between Good and Evil is personified by a combat between a griffin and a centaur at the Fountain of Destiny. Neither one can prevail on its own, but "The deeds of weak and mortal men can tip the scales one way or the other."

[[folder: {{Literature}}]]
* ''Literature/{{Animorphs}}'':
** Avoiding this trope is reason behind the CosmicChessGame the Ellimist and Crayak are playing. It's unclear whether it's even possible that either one can be killed in their [[AscendedToAHigherPlaneOfExistence present state]], but neither particularly want to try, since the collateral damage from such a fight would almost certainly annihilate the galaxy (at the very least).
** ''Megamorphs'' #2: The crab aliens can't get to the ant aliens' base without getting shredded by their energy weapons, the ants can't penetrate the crabs' force field.
* ''Literature/TheWitchlands'':
** No Threadwitch can see Threads (emotions and connections) of another Threadwitch, leaving master manipulators essentially incapable of acting against one another.
** Voidwitches can't use their powers on each other, so Bloodwitches can't puppet Weaverwitches and Weaveriwthces can't puppet Bloodwitches. Bloodwitches can handle any army Weaverwitches can throw at them, and Weaverwitches can keep throwing armies at Bloodwitches, leaving both in a stalemate.

* In an episode of ''Series/StarTrekVoyager'', the ship's doctor, a hologram-based artificial intelligence, encounters another such computer program that has become unhinged. When it strikes out at the Doctor's holographic image, the Doctor merely flickers. To demonstrate the futility of the situation, he tosses a nearby object at the other program, who also flickers. "This could get tedious." However, the other program then simply strikes the Doctor's portable holoemitter, knocking it off of him and deactivating him.
* In one episode of ''Series/{{Charmed}}'' Piper and Cole have a fight while both are invulnerable; Piper because [[GooGooGodlike her obscenely powerful unborn child]] was protecting her with a forcefield, and Cole because of the [[NighInvulnerable Nigh Invulnerability]] he acquired as part of the powers he absorbed while in the demonic afterlife. It took Leo chastising them on the pointlessness of their battle to end it.
* In an episode of ''Series/LoisAndClark'', some random dude off the street ends up with a carbon-copy of Superman's powers due to [[LightningCanDoAnything lightning]]. Said random dude then starts a Hero For Hire business, charging people premium rates for applying his superhuman powers, in between using his X-ray vision to [[PowerPerversionPotential check out girl's changing-rooms]]. Supes gets fed up with this pretty quickly and starts actively interfering in the 'business' (and pleasure), causing the dude to lose his temper and start a fight. Both of them, of course, are super-strong, but entirely invulnerable - and they're more invulnerable than super-strong, resulting in a mutually invulnerable brawl... the only possible loser being the surrounding area.
* ''Series/{{Caprica}}'' at one point had Zoe and Tamara fighting in V-World. In this case, they can hurt each other all they want, but neither of them can die since they're both digital avatars. The fight only ended when Zoe talked Tamara into an alliance.
* Battles between Ascended beings usually work out this way in the ''Franchise/StargateVerse''. Since they're EnergyBeings of equal stature, neither one can do anything to ''over''power the other, but they can keep the other sufficiently distracted as to be unable to do anything else. Both Anubis and Adria are taken care of by getting locked into an eternal fight with another Ascended.
** It is implied that Ascended beings can kill one another but only if one is vastly more powerful than the other, which is a very rare case but not impossible: belief can empower an Ascended, which is why they insist to everyone on the mortal planes that they're not gods. That was one of the causes for the ideological split between the Alterans and the Ori: the latter formed [[PathOfInspiration Origin]] [[AGodAmI specifically to gain even more power]], but the distance between the Ori galaxy and the Milky Way meant they were still too weak to overpower the Alterans... which is why they started converting the Milky Way's native population to Origin as well, abusing the Alterans' PrimeDirective to build up a power base in plain sight without a DeusExMachina to fear from.
* On ''Series/Preacher2016'', angels have the ability to instantly respawn, good as new, after dying. This gets PlayedForLaughs as Jesse and two angels get in a fight with a Seraphim, as they keep killing each other over and over again only to reappear and go right back into the fight while their dead former bodies keep piling up all over the place. They finally manage to restrain the Seraphim without killing her, and then Cassidy shows up and shoots her in the head, starting the whole thing over again.

[[folder: ProfessionalWrestling]]
* In {{Wrestling/ECW}} Rob Van Dam and Jerry Lynn usually started their matches with a series of Chain Wrestling moves which the other countered pretty quickly.

[[folder: TabletopGames]]
* In ''TabletopGame/DungeonsAndDragons'' edition 3.5, Damage Reduction involving alignments were included. There is a lot of infighting between demons and devils both between the two species and [[ChronicBackstabbingDisorder within their own ranks]]. However, high level demons and devils tend to have a lot of damage reduction, which can only be overcome with weapons that have the Good subtype. The same is true for Celestials vs Celestials, but they're less likely to fight.
* In ''TabletopGame/WarhammerFantasyBattle'' if two units both have Always Strike First, they either fight depending on their initatives or fight at the same time, depending on editions. Similarly, if two units both have the counter rule Always Strike Last, the same thing occurs. Note that in both cases, if the combat involves other participants who have neither rules, these occur before (if it's First) or after (if it's Last). If a model is granted both rules, they cancel eachother out (this usually occurs with any model armed with a great weapon and innately have Always Strikes First).

[[folder: VideoGames]]
* In ''VideoGame/MagicalStarsign'', elements have an ElementalRockPaperScissors going on, with exception of Light and Dark which are mutually weak to each other.
* In ''VideoGame/TeamFortress2'' this is the case with a few of the classes.
** Two Pyros will fall into this trope. Both are resistant to each other's signature ability (setting each other on fire), their unlockables are useless as the Flare Gun and Axtinguisher require their opponent to be on fire , meaning the winner is decided by either shotguns (if either has one equipped), flamethrowers (which would require either participant to move into the range of the other's flamethrower) or melee weapons (which do have some advantages over each other but don't make all that much difference).
** Demomen equipped with the Chargin' Targe might also qualify (since it increases their resistance to explosives and removes their ability to ambush enemies with sticky grenades).
** Engineers, as the most 'turtle" class, fall into this category as well, apart from a few equipment mismatches.
* In ''VideoGame/{{Pokemon}}'', many elemental types ([[FireIceLightning fire, electric, ice]], and so on) are resistant to attacks of their own element (receiving half normal damage). Bug and Fighting types are resistant to each other's element, and Normal and Ghost types are completely ''invulnerable'' to the other's element. Oddly Ghosts and Dragons are weak to their own element! A fight between such types, especially at low levels (where they're unlikely to know any other attacks), will often result in this. Some matchups involving Dual types can also cause mutual weakness.
** Wobbuffet is another example, as it learns no direct attacks whatsoever and is capable only of various {{Counterattack}}s. Pitting one Wobbuffet against another Wobbuffet will result in a stalemate where neither one can harm the other in any way (and in Generation 3, neither could be switched out for another fighter due to the ability Shadow Tag preventing doing so). However, once they both deplete their PP (which is going to be ''a while'') they will be forced to use Struggle. If they both held Leftovers, the damage taken from struggling was mostly negated, making the battle endless. This was rectified in Generation 4.[[note]] In Diamond/Pearl, using Struggle causes 1/4 of the user's max HP in recoil to the user, meaning any Pokemon with no remaining PP will faint quickly. Shadow Tag was fixed so that it is negated if the opponent also has it.[[/note]]
** Pit two Smeargles together and they can't do anything except futilely try to copy each other. Fortunately unlike with the Wobuffet case, they only have 1PP, so they start struggling quickly.
** And we musn't forget Ditto. Its only move is the ability to transform into the opponent, copying their appearance, stats (barring HP), and their moveset. Now, let's pit two Dittos against each other...
** Catch a Metapod/Kakuna, and they will only know ''Harden''. Pit them against another such enemy, and watch the epic contest unfold, just like in one of the early episodes of [[Anime/{{Pokemon}} the anime]].
* In ''VideoGame/EscapeFromMonkeyIsland'', you engage in a giant statue fight with the villain. Your life bars regenerate too fast for either side to win, so you have to figure out an alternate means to proceed.
* In ''VideoGame/{{Touhou}}'', mortal enemies Mokou and Kaguya, while not invulnerable as such to each other's attacks, are both immortal and will regenerate the wounds inflicted by the other. The result is a long-term stalemate where no matter who wins the individual battles (usually Kaguya), either of them will be back to start again in no time. Yet they keep on fighting to the "death", partly because Mokou just hates Kaguya ''that much'' and partly because they really don't have anything better to do.
* Knalgan [[MirrorMatch mirrors]] in ''VideoGame/BattleForWesnoth'' - a mirror match with a faction composed of highly defensive and slow dwarves, and fast but low-damage or frail outlaws. Neither side has and magic or poison needed to dislodge the other's defensive dwarves, and neither side has any Time-of-Day based powerphase advantage over the other. As a result, neither side has much incentive to attack.
* In the vast majority of {{MMORPG}}s there's the quintessential healer vs healer "battles". Extended in some cases when defensive non-healing classes and setups have some mean of regeneration and extreme defense (as opposed to healer's low defense and extreme regeneration).
* Protoss/Protoss and Zerg/Zerg {{Mirror Match}}es in ''VideoGame/Starcraft2'' are currently like this. Both tend to result in either one player losing almost instantly to a savvy rush (mutual weakness, more often in [=ZvZ=]) or both turtling massively for an excruciatingly long period until one makes a small mistake - and loses almost instantly (mutual invulnerability, more often in [=PvP=]). Terrans have a comparatively vast range of options for breaking a stalemate.
* [[http://www.youtube.com/watch?v=AUGCpClNgwQ This video]] should be a good demonstration of why holding a MirrorMatch between two [[VideoGame/FinalFantasyV Exdeath]] players in the ''VideoGame/DissidiaFinalFantasy'' series is a bad idea.
* In ''VideoGame/TheLegendOfDragoon'', each element takes double damage from it's opposite: [[PlayingWithFire fire]]/[[MakingASplash water]], [[BlowYouAway wind]]/[[DishingOutDirt earth]], [[LightEmUp light]]/[[CastingAShadow dark]]. The sole exceptions are [[ShockAndAwe lightning]] and [[InfinityPlusOneElement neutral]]
* The starting positions of England and France in ''VideoGame/EuropaUniversalis'' mirror the real life example above. France has the stronger army, but cannot bring it to bear because England the stronger navy. Can also happen when two nations share a more powerful ally. Neither can attack the other, because their shared ally would side with the defender.

[[folder: {{Webcomics}}]]
* The titular characters of the webcomic ''Webcomic/BobAndGeorge'' were immune to each others' powers due to being brothers. This is in turn a reference to [[Franchise/XMen Scott and Alex Summers]] being immune to the other's superpowers for the same reason.
* In ''Webcomic/ElGoonishShive'', the Immortal Pandora, and the Emissary of Magic [[http://www.egscomics.com/index.php?id=2218 confronted each other inside of Grace's dreams.]] Pandora was by far the more powerful of the two, so the Emissary could do nothing against her. However, as an Immortal, she was bound by rules preventing her from striking first, meaning that she could do nothing against the Emissary. When they realized that a fight wasn't feasible, they instead [[http://www.egscomics.com/index.php?id=2220 decided to talk.]]

[[folder: RealLife]]
* England vs. Louis XIV's France, ignoring the participation of Austria & co. for a moment. England had a very large, good navy and a tiny army; France had a large, okay-ish navy and a very large, decent-to-good army. Rinse and repeat right up to the end of the Napoleonic Wars. Britain vs The Dutch was the reverse, however; Holland had a ''tiny'' army, but Britain's navy was unable to get its act together for the most part. If there was a narrative pattern to Britain's participation in wars, it'd be having a great big navy that protects it from foes with great big armies - but, conversely, doesn't allow it much chance to really take the war to its land-based foes. A major factor in this was that as an island nation, a powerful and well-trained navy was a necessity, while the long-standing English distrust of standing armies made building a powerful army not just difficult but when not actively involved in a war ''undesirable''.
* A mention of the Peloponnesian War could probably go along with that France/England Hundred Years War example. Athens was a sea power and Sparta had the best land forces in Greece (Athens' walls prevented a direct Spartan attack). Sparta had to build a navy before it could successfully choke off Athens, almost 30 years in.
* The United Kingdom (and allied Commonwealth countries) versus Nazi Germany fell into this situation from 1940 (the fall of France) to the end of 1941. Both had to rely fighting around the peripheries (North Africa, and the North Atlantic Ocean) because neither could attack the other directly aside from bombings which didn't have that much of an effect. The Allies could have controlled the English Channel to allow an attempted landing, but had nowhere near the ground forces or equipment necessary to make it successful. The Germans had enough troops to conquer Great Britain, but had no way of forcing a crossing of the Channel to get them there.
* The Battle of Hampton Roads, a naval battle of the American Civil War, featured the first engagement between ironclad warships--the USS ''Monitor'' and the CSS ''Virginia''. The two ships spent three hours NoSell-ing each other's attacks before withdrawing.

!!Mutual weakness:

[[folder: Fan Fiction]]
* Luffy and Crocodile in ''[[https://www.fanfiction.net/s/11961369/19/Blood-Man-Luffy Blood Man Luffy]]'' both have devil fruits that exploit the weaknesses of each other. As a blood man, Luffy can easily coat himself (or Crocodile) in blood so Crododile can't disperse into sand, but as a sand man, Crocodile can completely dry out Luffy with a touch of his hand.
* When they finally fight in ''[[https://www.fanfiction.net/s/11171261/58/Free-from-Force Free from Force]]'', Anakin and Palpatine are incapable of predicting each other's attacks due to Anakin temporarily cutting himself off from the Force to save Padme's life. Since Anakin can't use the Force, he can't use CombatClairvoyance but neither does he have a presence in the Force to sense.

[[folder: {{Film}}]]
* In ''Film/{{Star Trek II|The Wrath of Khan}}'', the still badly-damaged ''Enterprise'' leads the less-damaged ''Reliant'' into the Mutara Nebula. When Saavik points out that the nebula will disable shields and sensors on any ship that enters, Spock answers "Sauce for the goose, Lieutenant. The odds will be even."

[[folder: LiveActionTelevision]]
* On ''Series/TheBigBangTheory'', Sheldon and Barry compete over who gets a new office. Since there is not much either one is equally good at, they decide to settle it at something they are equally bad at - namely, sports. So they head to the gym to play a one-on-one basketball game. Unfortunately, they are so equally bad at it that neither one can score a single basket. Eventually, they settle on bouncing a ball in the air and whoever bounces it higher gets the office. Sheldon wins by sheer luck. ("Who's unsatisfactory in P.E. now?")

[[folder: VideoGames]]
* Also in the ''VideoGame/{{Pokemon}}'' series, Ghost- and Dragon-typed Pokémon are notably vulnerable to their own element, especially the Dragons as they are the only element that Dragon-type attacks get an advantage against at all. It is also common competitive practice to teach a given Pokémon moves from other elements specifically to counter the types they are weak against (such as giving a Fire-type user the Grass-type "Solarbeam" for use against Water-, Rock- and Ground-types).
** Due to the complicated nature of ElementalRockPaperScissors, Pokémon with dual elemental types can in fact become vulnerable to one of their own elements (like the Rock+Flying Aerodactyl being vulnerable to Rock attacks, or the Fighting+Steel Lucario being vulnerable to Fighting attacks).
** When you start dealing with dual-typed Pokemon, there are a lot of possible matchups between different Pokemon that are weak to one of their opponent's types and strong against another (like the Dark/Fire Houndoom versus the Water/Ghost Jellicent - Water beats Fire and Dark beats Ghost).
*** Subverted with the final evolutions of the three starters in [[VideoGame/PokemonXandY the 6th generation]]. Chesnaught is Grass/Fighting, Greninja is Water/Dark, and Delphox is Fire/Psychic.[[note]]Grass beats Water beats Fire, but Fighting beats Dark, Dark beats Psychic, and Psychic beats Fighting.[[/note]]
** ''VideoGame/PokemonDiamondAndPearl's'' use of dual-typed starter Pokémon provides an interesting scenario, where each member of the starting trio ultimately acquired a secondary type that could counter the opposing element: Torterra's Ground typing can counter Infernape's Fire, Infernape's Fighting type can counter Empoleon's Steel, and Empoleon's Steel at least removes its normal weakness to Grass (but also adds in a weakness to its Ground). Infernape was still [[GlassCannon the fastest of the bunch]], though, sometimes capable of knocking the opponent out before they could even throw their first attack. As well, Empoleon could easily learn Ice Beam, letting it deal four times normal damage to Torterra, as opposed to the normal two times a regular Grass-type would suffer.
** The Gastly family is interesting in particular in that the only targets they deal super-effective damage to with Ghost-type attacks - that is, Psychic and Ghost - do super effective damage to them as well.
** Water Pokémon are weak to Grass moves. Nearly all Water-type Pokémon can learn at least one Ice-type move, which Grass-type Pokémon are weak to.
** In generation 1, Bug type Pokemon were weak to Poison attacks, while Poison type Pokemon were weak to Bug attacks. In Generation 2, this was changed to Bug being resisted by Poison and Poison doing neutral damage to Bug for reasons unknown.
* The Undead and Drake [[MirrorMatch mirrors]] in ''VideoGame/BattleForWesnoth'' - most Undead units are vulnerable to the same faction's magical Dark Adept unit and its Arcane damage, and similarly all Drake units are vulnerable to that faction's magical Cold damage dealing Saurian Augur. Both the Adept and the Augur, however, are SquishyWizard units vulnerable to the conventional attacks of their respective faction. The result is Mutual Weakness.
* Class versus Class battles in ''VideoGame/TeamFortress2'' not described above are more of a mutual weakness, coming down to who has the better aim, ping, and/or luck (Sniper wars in particular). The Half-Zatoichi deliberately invokes this, as it has a special ability where it will OneHitKill anyone else who also has the weapon out.
* In many ''Franchise/FinalFantasy'' games, the air/wind element is often vulnerable to itself, inflicting greater damage on flying enemies. Also, Fire and Ice elements are usually vulnerable to each other.
* In ''VideoGame/FinalFantasyTactics'' characters could receive attack (or defense) bonuses depending on each fighter's astrological sign -- however, the bonus always applied both ways.
* In the ''VideoGame/DissidiaFinalFantasy'' [[DivineChessboard campaign modes]], the player would sometimes happen upon a golden Manikin piece (generally optional encounters guarding valuable equipment). These units tend to be equipped in such a way that their health is critically low, but are augmented in other ways (such as having nigh impenetrable Bravery defense, or having summons that they immediately use to send their own Bravery points through the roof), meaning that the first HP attack to connect is generally the one that wins the match.
* In ''Franchise/FireEmblem'' Divine Dragon manaketes are specialized in dealing damage against other dragons/manaketes. While Divine Dragons [[AlwaysLawfulGood are never enemy units]] in the main game (save for DLC chapters and the Wellspring of Truth), both ''VideoGame/FireEmblemShadowDragon'' and ''VideoGame/FireEmblemAwakening'' have a multiplayer where Divine Dragon Manakete units can face against each other. The latter also introduces the Taguels who deal effective against all beast units. Like the Manaketes, they're only encountered as enemies in multiplayer [=SpotPass=] material, Yarne's recruitment chapter, and the Wellspring of Truth.
** ''VideoGame/FireEmblemFates'' introduces the new class Kinshi Knights, which are essentially Pegasus Knights that can wield bows, the very weapon they are most vulnerable to. Their Air Superiority skill also makes them very effective against other flying units, but it cancels itself out if both sides have it.
* A common tendency in the ''Franchise/ShinMegamiTensei'' series is the tendency for demons with a clear specialty in one element to always be weak to its opposite. For instance, Pyro Jack is clearly a [[PlayingWithFire fire]] demon while Jack Frost is clearly an [[AnIcePerson ice]] demon, and both are weak to each other. Hence, the only advantage one of the two would have over the other is for Pyro Jack to typically be at a higher level. A similar occurrence happens between [[ShockAndAwe lightning]] demons and [[BlowYouAway wind/force]] demons as well as between [[LightEmUp expel]] demons and [[CastingAShadow death]] demons. [[DownplayedTrope Do NOT take this as a rule for the whole game though.]] That would likely result in a very quick death if one isn't careful.
* In ''VideoGame/DungeonFighterOnline'', two classes (intended for use as alts) are banned from [[PlayerVersusPlayer PvP]] because fights involving them won't be much fun for anybody. Dark Knights can throw powerful combos out with minimal player effort (after preparation pre-fight) but have a very limited moveset in any given fight and will quickly become predictable. They're also ''dependent'' on flashy powerful combos, with limited defense past that spectacular offense. Creators, despite having plate-equivalent armor and decent health, have relatively limited damage output and no real mobility or evasion powers; they need time to finish an opponent and likely won't last long after receiving an initial hit. They also can wall their opponent away from them, can hit from ''any relative position'' on the screen, can likewise grab from anywhere, and a Creator's basic attack is an infinitely-chainable telekinetic strike which acts as a ComboBreaker, can air juggle, and is useable while in stunlock, prone, asleep, confused or paralyzed. "Sudden death" is an apt description of a hypothetical match against a Creator, one way or another.
* The characters of the realism-based ''VideoGame/Insurgency'' are so weak that everyone, even armored targets, are frequently killed with one or two shots, especially if armor-piercing ammo is used.
** Additionally, the use of flashlights or tracer rounds may count: For the former, the position of enemies can be revealed more easily at the cost of exposing your own position, while tracer rounds help show when you're running low on ammo [[DepartmentOfRedundancyDepartment at the cost of showing when you're running low on ammo.]]

[[folder: RealLife]]
* In RealLife, the concept of idea of [[http://en.wikipedia.org/wiki/Mutual_assured_destruction mutual assured]] [[MutuallyAssuredDestruction destruction]] is the reason the Cold War "remained cold"; if either the U.S. or Russia launched a nuclear attack, the other side would have enough time to launch a nuclear counterattack and hit the other side just as hard.
** This was part of the reason why both the arms reduction treaties were so fiercely contested and submarine-launched missiles were so nerve-wracking, as both of them threatened to eliminate this mutual disadvantage (the former by getting one side or the other to start thinking "Hey, maybe we won't lose everything if we attack right now", the latter by potentially reducing the amount of time you have to detect a hostile nuke heading for you to detect it and respond from an hour to just fifteen minutes).
** This is still generally the reason ''nobody'' uses nuclear weapons in the modern age: even if you did launch a nuke at somebody else, they'd just lob a nuke right back before yours got there, and then you'd both be dead.
** This also served as the central conflict in the film ''Film/WarGames'' when the WOPR supercomputer (with access to real nukes) was instructed to play a simulation called "Global Thermonuclear War". In the end, it memorably declared "The only winning move is not to play."
** To a lesser extent, chemical weapons. Their main tactical benefit rather quickly shifted from killing huge numbers of enemy troops outright to forcing enemy troops to cover themselves in heavy, encumbering protective clothing that hugely reduced their combat-effectiveness... But unfortunately this inevitably meant that ''friendly'' troops in the same area were equally encumbered, and some of the nastier and more persistent agents like VX would hang around for ''weeks'' after deployment and were even more ecologically destructive than nuclear fallout, rendering the newly conquered territory pretty much worthless.[[note]]This latter point was especially important to the Soviet Union, with their centrally-mismanaged agricultural sector and the constant spectre of food shortages it created.[[/note]]
* Any duel with lethal weapons where the participants are not wearing armor can become this, especially if the weapon style is focused on offense. For example, a LOT of serious rapier duels ended with either two people dead, or one dead and one crippled.

!! Pair-based systems

[[folder: TabletopGames]]
* In ''TabletopGame/DungeonsAndDragons'' 3rd edition:
** Fire/Cold, [[GoodHurtsEvil Good]] / [[AllergicToEvil Evil]] and [[OrderVersusChaos Lawful/Chaotic]] effects are particularly effective against creatures who embody the opposite element, and do not affect creatures who embody the same element. A creature who is both Good and Evil or Lawful and Chaotic (such as a FallenAngel or AscendedDemon) gets both sets of vulnerabilities, but a creature who embodies both Fire and Cold is immune to both.
** Living creatures (and [[TabletopGame/{{Eberron}} deathless]]) are powered by positive energy (which heals them) and harmed by negative energy, while [[ReviveKillsZombie undead are affected in the opposite manner]]. Undead who can manipulate negative energy are more common than living creatures who can manipulate positive energy, however.
** Some Air creatures take penalties when defending against Earth effects and vice versa, but this is applied less consistently than the above dualities, largely because Earth and Air rarely exist as PureEnergy.

[[folder: VideoGames]]
* ''VideoGame/ChronoCross'' had three sets of opposing elements (Red/Blue, Green/Yellow, Black/White), each dealing increased damage to its opposite and reduced damage to itself; every character in the ([[LoadsAndLoadsOfCharacters rather large]]) roster was assigned an elemental affinity.
* ''VideoGame/FinalFantasyX'' and [[VideoGame/FinalFantasyX2 its sequel]], although the player characters were NonElemental by default, elements were arranged in pairs (Fire/Ice and Water/Thunder) with each doing increased damage to its opposite. The player could also find (or [[ItemCrafting customize]]) weapons and armor with elemental affinities, which could create scenarios of mutual weakness or invulnerability depending on what was equipped at a given time.
* ''VideoGame/TheLegendOfDragoon'' had pairs of opposing elements (Fire/Water, Earth/Wind, Light/Dark) doing increased damage to each other, reduced damage to itself; the Thunder element had no opposite, but also shared reduced damage against itself. Every character (and most monsters) had an elemental affinity, and each character's strongest armor (the "DG armor" series) would completely nullify damage from their own element.
* ''VideoGame/ShadowHearts'' has Fire/Water, Earth/Wind, and Light/Dark. The pairs do increased damage to each other, and there are spells that add elemental status to your weapons. In each game, you acquire one character of each element (and in the second and third game, a NonElemental character); each character's ultimate armor allows them to resist their opposing element.